The use of platforms that roll along a conveyor or in production line for assembly manufacture is disclosed in Federal Republic of Germany Patent Document OS 38 40 256, in which passenger cars are transported during their assembly. At the ends of the production line, transfer stations are necessary so that the platforms, also known as skids, can be transported back to the starting point of the production line over a parallel path. Transfer stations can also be used to transfer a platform to another conveyor that is part of a different section of the assembly line.
Typically, the platform or skid is propelled or displaced along the conveyors using driven friction wheels which are positioned along the conveyor and engage the sides of the platform, thereby driving it along the conveyor. The use of such driven friction wheels permits the platform to have a relatively low structural height. Driven friction wheels can also be used at transfer stations where the direction of travel of the platform is changed; however, because the friction wheels must contact a side surface of the platform, the friction wheels usually interfere with the movement of the platform when its path of travel is changed at a transfer station. As a result, it is typically necessary to lift the platform to avoid the friction wheels and, thereafter, to lower the platform once the platform has passed over the friction wheels.